Barry asked:

What were the influences of Aristotle on Thomas’s Philosophy?

Answer by Tony Fahey

Barry, whilst this is an interesting question, I’m afraid to chronicle the influences of Aristotle on the works of Aquinas is so comprehensive that it is beyond the space available to me in this forum. That being said, since it is such an interesting issue, I have identified what I believe may be some of the more interesting of these influences on Aquinas of the person whom he called ‘The Philosopher’.

Aristotle, Aquinas, and the existence of God

The cosmological or causal argument for the existence of god takes the view that there must be a cause either in the sense of a prior event, or a reason for the occurrence of an event. That is, there must be a reason or cause for everything that happens. If we trace back from effects to their causes, we can either continue indefinitely, or reach a point where we are forced to acknowledge that there must be an ultimate or first cause – some point from which everything begins. The cosmological argument is that this first cause is God.

Amongst those philosophers and theologians that make the cosmological argument for the existence of God are Aristotle and Aquinas. Aristotle calls the first cause the ‘Prime Mover’. But it is a prime mover which itself does not move. There is a God, says Aristotle (for how else does motion begin?), but god himself is changeless. He is the final cause of nature, the drive and purpose of things, the form of the world, the principle of life, and the sum of its vital processes and powers – but he does not move.

Aquinas put forward his arguments for the existence of god chiefly in his two main works, the Summa Theologiciae and the Summa contra gentiles. In the Summa Theologiciae he presents his ‘five ways’ to demonstrate the existence of God. The first way is called the argument from motion, which is better understood as ‘change’. It is in this first way that Aquinas follows Aristotle’s ‘prime mover’ thesis. Aquinas begins by claiming that it is evident that some things are in the process of change. Change, or motion, he says, is an observable fact. It is important to say that Aquinas does not say that everything changes, but that some things sometimes change. Aquinas believes that change requires an explanation – a cause. Change, he says, must either come from chance or design, but he rules out the possibility that change is explainable by chance. If change occurs, he concludes, it must be caused.

Following Aristotle, Aquinas concludes that for any change there must be a first principle that causes the change, but which itself is unchanged. This first principle, he claims, is God. God is the cause of change that is not itself changed. This is what everyone understands as god. Therefore God exists.

Before continuing with further examples of Aristotle’s influence on Aquinas, it should be pointed out that many philosophers (and some theologians) have great difficulty in accepting this cosmological argument. For example, the first difficulty is in the assumption that anything requires a cause. Aquinas rules out the possibility of random or accidental change. Whilst it might be the case that things cause one another, it could still be argued that the cause of events is mere chance and is not connected to a continuous link to a first cause.

Probably the most convincing argument against Aquinas’s cosmological argument is presented by Anthony Kenny in his book The Five Ways. Aquinas, he says, depends for his first argument of causation on Aristotle. According to this analysis, the cause of change must possess a property which will initiate the change. For example, for something to become hot, the thing that causes the change must itself possess the property of heat. But modern science rejects this argument. The grain which makes a cow fat is not itself fat, and microwaves can generate heat without themselves being hot. Aquinas, says Kenny, is not giving a straightforward metaphysical analysis, but an analysis which presumes a classical, and discredited, physics.

More on the influence of Aristotle on Aquinas

Like Aristotle, Aquinas holds that the basis of human knowledge is experience – as Aristotle so famously says, ‘nothing is found in the intellect which was not found first in the senses’ (‘Nihil est in intellectu quin prius fuerit in sensu’). The fact that our knowledge derives from experience does not mean that it ends there. A deeper understanding of the world comes from using the thinking faculty of our minds (the intellect) to bear on our sensory experience, so that we may form ideas, combine them into propositions, and then to reason on the basis that these propositions to develop our knowledge still further. Thus, while Aquinas is an empiricist, he rejects the limitations that Hume imposed on reason, while he is a rationalist, he does not abandon human knowledge’s moorings in the sensible order.. That is, that the mind possesses the innate power to discriminate and to assimilate information. A process altogether different to Plato’s notion of specific innate knowledge expounded in his theory of ideal forms.

As shown above, for Aquinas, as it was for Aristotle, there is nothing in the mind that is not first in the senses. The human mind, he says, has the capacity to separate out – to abstract – the form from the particular conditions in which we find it, so that we can consider the form as a thing apart. However, it is we ourselves, in virtue of the mind’s abstractive power, who give this quality or property a new existence in the mind: a mental existence, as a concept or idea, which has now been withdrawn from its particular material conditions. Aristotle calls it an ‘incorporeal’ or ‘im-material’ state, in the sense that the form is no longer subject to the particular material/corporeal conditions in which we originally found it bound up with matter. Moreover, once formulated, we can turn to attribute this property to particular people or actions we later encounter. That is, we ‘re-cognise’ it when we encounter it in other individual cases in our daily lives.

Again following Aristotle, Aquinas holds that all living things have souls. The difference between human beings and animals and vegetables was not that they had a soul, but that they had a rational or intellectual soul. For Aquinas, body and soul are not the same as matter and form: the soul is related to the body as form is to matter. The body of human beings, as with all material things, is made up of matter and form. It is the form of the human body that is the human soul, not the form of the matter that constitutes the body. For Aquinas there is primary matter and secondary matter. Primary matter is air, earth, fire and water. Secondary matter is the entity constituted by primary matter. In the case of human beings, the human body represents secondary matter infused with a form, the human soul, which is particular to itself.

Like Aristotle, Aquinas holds that Plato’s concept of universal ideas existing in a non physical or non corporeal realm is wrong. However, in this instance, while, like Aristotle, he thinks that there are no innate ideas as such, he does not believe that sensory experience on its own was enough to explain the origin of ideas. Thus, Aquinas can be said to fall somewhere between empiricists and rationalists. That is, like empiricists he believes that initially the mind is a tabula rasa; and like rationalists he holds that experience alone does not account for that which appears on the blank slate.